PROJECT SUMMARY/ABSTRACT Dementia affects over 5 million older adults in the US, with vast implications for individual patients, their families, and social programs. Research to date has not fully clarified the role that multiple co-occurring chronic conditions (multimorbidity) play in the development of dementia. Many of the most prevalent chronic conditions have therapeutic pathways and thus to the degree that they contribute or are intrinsic to the progression from mild cognitive impairment (MCI) to dementia, represent tractable targets for dementia intervention. As a result, there is a need for greater understanding of the complex interactions between existing morbidity combinations, cognitive impairment, and progression to dementia and evaluate whether these multimorbidity combinations are more likely to occur among older adults from underrepresented racial/ethnic backgrounds. Our proposed work advances this research by asking: (1) Are there specific multimorbidity combinations associated with accelerated cognitive decline? (2) Are minority older adults with particular multimorbidity combinations more likely to transition from mild cognitive impairment to dementia? (3) Are concurrent changes in cognition and function influenced by specific multimorbidity combinations? And, (4) Do minority older adults with specific multimorbidity combinations have higher hospital/nursing home use following dementia onset? The proposed work will provide important insights and inform policies and programs that seek to delay costly and intensive levels of care among older adults by identifying disease combinations associated with rapid cognitive decline and dementia onset and progression. Our proposed research enables the study of long-term changes in cognition in over 20 years of nationally-representative biennial data (~38,000 people in the Health & Retirement Study), and 5 years of annual data (~9,700 people in the National Health & Aging Trends Study). We propose three aims: Aim 1. Determine how the cognitive impairment trajectory is modified by multimorbidity combinations. Aim 2. Determine how dementia onset is modified by multimorbidity combinations. Aim 3. Determine how the burden of health care utilization after dementia onset is modified by multimorbidity combinations.